In the normal human heart, the sinus node, generally located near the junction of the superior vena cava and the right atrium, constitutes the primary natural pacemaker initiating rhythmic electrical excitation of the heart chambers. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers, causing a depolarization known as a P-wave and the resulting atrial chamber contractions. The excitation pulse is further transmitted to and through the ventricles via the atrioventricular (A-V) node and a ventricular conduction system causing a depolarization known as an R-wave and the resulting ventricular chamber contractions.
Disruption of this natural pacing and conduction system as a result of aging or disease can be successfully treated by artificial cardiac pacing using implantable cardiac stimulation devices, including pacemakers and implantable defibrillators, which deliver rhythmic electrical pulses or anti-arrhythmia therapies to the heart at a desired energy and rate. A cardiac stimulation device is electrically coupled to the heart by one or more leads possessing one or more electrodes in contact with the heart muscle tissue (myocardium). One or more heart chambers may be electrically stimulated depending on the location and severity of the conduction disorder.
A stimulation pulse delivered to the myocardium must be of sufficient energy to depolarize the tissue, thereby causing a contraction, a condition commonly known as “capture”. In early pacemakers, a fixed, high-energy pacing pulse was delivered to ensure capture. While this approach is straightforward, it quickly depletes battery energy and can result in patient discomfort due to extraneous extracardiac stimulation, e.g., of surrounding skeletal muscle tissue, the patient's phrenic nerve or the patient's diaphragm.
The “capture threshold” is defined as the lowest stimulation pulse energy at which capture occurs. By stimulating the heart chambers at or just above this threshold, comfortable and effective cardiac stimulation can be provided without unnecessary depletion of battery energy. The capture threshold, however, is extremely variable from patient-to-patient due to variations in electrode systems used, electrode positioning, physiological and anatomical variations of the heart itself, and so on. Furthermore, a capture threshold may vary over time within a patient as, for example, fibrotic encapsulation of an electrode can occur after implantation of the electrode.
Implantable lead(s), attached to an implantable cardiac device (ICD), such as a pacemaker, is/are used to deliver such stimulation pulses to the myocardium. Some such leads are Multi-Electrode Leads (MELs), meaning they include multiple electrodes for use in pacing and/or sensing. MELs allow for more flexibility in pacing and sensing, as compared to single electrode leads. Generally, the more electrodes on a lead, the more flexibility provided. However, a challenge when using leads with greater numbers of electrodes is increased complexity when setting up the electrode configuration. For example, one left-sided lead design includes four electrode arrays (also referred to as groups or bands) with four electrodes each, thus resulting in a single lead with sixteen electrodes. An example of an electrode that can include sixteen (and even more) electrodes is disclosed in U.S. Patent Publication No. 2006/0058588 (U.S. patent application Ser. No. 11/219,305), entitled “Methods and Apparatus for Tissue Activation and Monitoring” (Zdeblick), published Mar. 16, 2006 (filed Sep. 1, 2005), which is incorporated herein by reference. With such a complex MEL there can be hundreds and possibly thousands of different cathode-anode combinations (also referred to as cathode-anode electrode configurations).
Presuming it takes on the order of about 90 seconds to test each possible cathode-anode electrode configuration, it would take hours upon hours for a clinician to test all possible electrode configurations for MELs having numerous electrodes. This would be true even if the clinician used an auto set-up programmer, if the programmer were to try to test all possible combinations.
Another challenge when using leads with greater numbers of electrodes is the limitation to the number of groups of electrodes that can be programmed in a single pacing cycle. This limitation poses a drastic drawback on the system because fewer groups of electrodes can be programmed in a single pacing cycle and to program more groups of electrodes requires two or more pacing cycles. This poses a problem because it may leave the patient paced in an undesired configuration for a pacing cycle. This may cause phrenic stimulation, triggering the patient to hiccup every time (or at least some of the times) the lead is programmed. This can occur as little as every follow-up, or as much as once daily during a daily lead configuration check and/or reprogramming.
Accordingly, it would be beneficial if more efficient methods and systems were developed for assisting with the configuration of such MELs.